1. Field of the Invention
This invention relates generally to temperature controllers and, more particularly, to temperature controllers that monitor and control the temperature of a home appliance such as a baking or broiling oven or the like.
2. Prior Art
Temperature controllers for appliances are well known and use various systems ranging from bimetallic strips to digital control systems that operate on a signal received from a thermal sensor to control temperatures. While such systems do provide a way to control temperature, the mechanical bimetallic strip based systems must be carefully designed to provide the required accuracy and are not readily adjustable if, for example, a temperature offset or other recalibration is desired. The microprocessor based systems provide good accuracy and control flexibility, but require relatively complex hardware or software to compensate for the nonlinearities and manufacturing tolerances of the temperature sensors used in the system. Typically, in such systems the temperature-resistance or temperature-voltage characteristics of a sensor are mapped into a look-up table, or a nonlinear equation defining those characteristics is determined. The system then either utilizes the look-up table to determine a temperature based on the input voltage or solves the nonlinear equation to determine the temperature. However, the provision of sufficient memory to define a look-up table having the required accuracy, or the provision of computing capability to solve a nonlinear equation adds complexity to the system, and also makes providing a temperature offset more difficult.
Microprocessor controlled systems of the type described above generally control the application of energy to a heating device, for example, by controlling a gas valve that controls the application of gas to a burner or by controlling a switching device that applies electrical power to a heating element. In such systems, it is desirable to monitor the status of the energy controlling devices used in the system to assure that energy is applied to the heating device only when called for. This has been done in the past utilizing optical couplers to isolate the electrical switching devices from the sensing circuitry to prevent the high voltages controlled by the switching devices from damaging the sensing circuitry or being a hazard to the user. Unfortunately, such optical isolators add cost to the system.